noble metal"In chemistry, the noble metals are metals that are resistant to corrosion and oxidation in moist air (unlike most base metals). The short list of chemically noble metals (those elements upon which almost all chemists agree) comprises ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au). More inclusive lists include one or more of mercury (Hg), rhenium (Re), and copper (Cu) as noble metals. On the other hand, titanium (Ti), niobium (Nb), and tantalum (Ta) are not included as noble metals although they are very resistant to corrosion." - (en.wikipedia.org 17.09.2019) Metal Gold Platinum group Silver